As transistors are miniaturized in size, a thin film such as an insulating film constituting a sidewall spacer (SWS) of a gate electrode requires a low film forming temperature, an improved resistance to hydrogen fluoride (HF), and a low dielectric constant. Thus, as the insulating film, a silicon carbonitride film (SiCN film) in which carbon (C) is added to a silicon nitride film (SiN film), a silicon oxycarbonitride film (SiOCN film) in which oxygen (O) is added to the silicon carbonitride film, or the like is used. In many cases, these insulating films are formed by an alternate supply method of alternately supplying different kinds of processing gases in that high step coverage property is required.
For the insulating film such as the above-described SiCN or SiOCN film, in order to further improve the resistance to HF, it is effective to reduce the oxygen concentration in the film by increasing the carbon concentration in the film. On the other hand, for such an insulating film, in order to further reduce the dielectric constant, it is effective to increase the oxygen concentration in the film by reducing the carbon concentration in the film. Recently, the demand for a film having an improved resistance to HF and a reduced dielectric constant, which are in a trade-off relationship, is increasing. However, it is difficult to satisfy the above-described demand for the film only by adjusting the composition of the SiCN film or SiOCN film, that is, by controlling the carbon concentration, the oxygen concentration, and the nitrogen concentration in the film. In addition, although a low film forming temperature is required when the insulating film constituting a sidewall spacer and the like is formed, the film forming temperature in the conventional alternate supply method is 600 degrees C. or so, and it was difficult to form the thin film such as the above-described insulating film in a low temperature range, for example, of 550 degrees C. or less.